Ag_(2)Sb合金单层上多层酞菁氧钒分子的组装

Assembly of multilayer phthalocyanine vanadium oxide molecules on Ag_(2)Sb alloy monolayer

利用低温扫描隧道显微镜(STM)研究了各种覆盖度下酞菁氧钒(VOPc)分子在Ag_(2)Sb/Ag(111)上的吸附行为和组装结构.不同于Ag(111)表面,当分子覆盖度在一个单层之内,吸附的VOPc分子均组装为有序的薄膜,呈现出规则排列的空隙和正方形单胞.通过扫描亚分子分辨的STM形貌图,揭示了正方形单胞由一个中心分子和四个对称排列的角分子组成;所有VOPc分子均采用O-up构型,并呈现出两种吸附取向,分子横轴相对于单胞侧边分别旋转约11°和21°.因分子间的偶极-偶极相互作用,进一步沉积的VOPc分子组装为具有O-down和O-up构型交替堆积的分子膜,在分子层内分子轨道沿π堆积方向发生重叠.该研究为调控金属表面功能有机分子组装膜的结构和组装行为提供了一种新途径.

Fabricating ordered molecular films and further tuning their assembly behavior is important for constructing organic devices with diverse performances.By using high-resolution scanning tunneling microscopy,in this work,we demonstrate that well-organized vanadyl phthalocyanine(VOPc)films can be formed via‘bottom-up’molecular self-assembly on a binary alloy Ag2Sb/Ag(111).The Ag2Sb monolayer is prepared by evaporating Sb atoms on clean Ag(111)and followed by annealing.The VOPc molecules are deposited on the Ag2Sb layer via thermal evaporation.The molecular configuration,structural and orbital characteristics of VOPc are clearly clarified at a submolecular level.It is found that initially the ordered VOPc membrane only exhibits the O-up adsorption configuration.Its square-shaped unit cell consists of five VOPc molecules where two adsorption orientations coexist with the horizontal axis of VOPc which is rotated by about 11°or 21°relative to the side of the unit cell.Due to the molecular dipole-dipole interaction,further-deposited molecules result in the assembly of the second-layer VOPc films with the O-down configuration and the square-shaped unit cell that contains only one VOPc molecule.Subsequently,due to the dipole-dipole interaction between layered molecules,following VOPc molecular layers adopt alternating O-up and O-down configurations as well as the square-shaped unit cell,similar to the case of the second layer.In addition,we find that the molecular orbitals overlap in each assembled molecular layer due to the π-π interaction which could facilitate the charge transport along the π stacking direction of VOPc.This research provides possibility to regulate the adsorption configuration and assembly behavior of functional organic molecules on metal surfaces by forming surface alloys.